Process for separation of tetrafluoroethylene from carbon dioxide using ionic liquids

ABSTRACT

A process for separating tetrafluoroethylene from a mixture comprising tetrafluoroethylene and carbon dioxide by contacting the mixture with at least one ionic liquid.

This application claims the benefit of U.S. Provisional Application No.60/857,566, filed Nov. 8, 2006, which is incorporated in its entirety asa part hereof for all purposes.

TECHNICAL FIELD

This invention relates to a process for separating tetrafluoroethylenefrom a mixture comprising tetrafluoroethylene and carbon dioxide (CO₂).

BACKGROUND

Tetrafluoroethylene (C₂F₄, TFE, or FC-1114) is the monomer used toproduce polytetrafluoroethylene (PTFE). TFE is highly explosive,flammable, and toxic. In order to prevent TFE from polymerizingunexpectedly while being stored, the TFE is inhibited with eitherhydrogen chloride (HCl) or carbon dioxide (CO₂). TFE and CO₂ havesimilar boiling points and also form an azeotrope, making a mixture ofthese components difficult if not impossible, to separate (see U.S. Pat.No. 5,345,013). Methods that are currently used for separating TFE fromCO₂ include membrane permeation, and caustic scrubbing. Following theseprocedures, the TFE-containing stream can then be processed, forexample, to produce a fluoropolymer or copolymer, such as PTFE. Thecurrent processes for recovering TFE from CO₂ suffer either from highvariable cost (caustic scrubbing), high CO₂ level in the product(membrane permeation), or multiple unit operations when additional stepsare added to address the primary deficiencies.

An alternative approach to separating TFE from CO₂ employs extractivedistillation or absorption using at least one ionic liquid as anentrainer or absorbent, respectively. U.S. Provisional Application No.60/719,735 describes the use of separation processes to separatecomponents of mixtures, wherein said mixtures comprise at least onehydrofluorocarbon compound, and may additionally comprise a gas such asCO₂. A need nevertheless remains for processes adapted specifically tothe separation of TFE from CO₂.

SUMMARY

The inventions disclosed herein include processes for the separation ofTFE from CO₂, processes for the preparation of products into which TFEcan be converted, the use of such processes, and the products obtainedand obtainable by such processes.

Features of certain of the processes of this invention are describedherein in the context of one or more specific embodiments that combinevarious such features together. The scope of the invention is not,however, limited by the description of only certain features within anyspecific embodiment, and the invention also includes (1) asubcombination of fewer than all of the features of any describedembodiment, which subcombination may be characterized by the absence ofthe features omitted to form the subcombination; (2) each of thefeatures, individually, included within the combination of any describedembodiment; and (3) other combinations of features formed by groupingonly selected features of two or more described embodiments, optionallytogether with other features as disclosed elsewhere herein. Some of thespecific embodiments of the processes hereof are as follows:

One such embodiment of the processes hereof provides a process forseparating tetrafluoroethylene from a mixture comprisingtetrafluoroethylene and carbon dioxide by contacting the mixture with atleast one ionic liquid in which carbon dioxide is soluble to a greaterextent than tetrafluoroethylene, and separating the tetrafluoroethylenefrom the mixture. In a further embodiment, the ionic liquid can includea cation selected from the group consisting of pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium,oxazolium, triazolium, phosphonium, and ammonium, as more particularlydescribed below.

When a separation process hereof is performed by using a technique suchas extractive distillation, the process may also involve steps such asadjusting the temperature and/or pressure of the mixture to be separatedand/or the feed of ionic liquid.

A further embodiment of the processes hereof provides a process forpreparing a fluorinated polymer or copolymer by separating TFE from amixture thereof with CO₂ by contacting the mixture with one or moreionic liquids, recovering the TFE, and subjecting the TFE to apolymerization reaction to prepare a fluorinated polymer or copolymer.

In another embodiment, this invention provides a kit that includes afirst container that contains a mixture of TFE and CO₂, a secondcontainer that contains one or more ionic liquids, and a connector toconnect the first container to the second container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a simple extractive distillationsystem.

FIG. 2 is a schematic diagram of a simple absorption system.

DETAILED DESCRIPTION

The present invention provides a method for separatingtetrafluoroethylene from a mixture containing carbon dioxide andtetrafluoroethylene by a separation technique in which at least oneionic liquid is used as a mass separating agent. Techniques useful forperforming such a separation include extractive distillation orabsorption. In particular, the present invention provides a method forseparating tetrafluoroethylene from a mixture comprisingtetrafluoroethylene and carbon dioxide comprising contacting the mixturewith at least one ionic liquid in which carbon dioxide is soluble to agreater extent than tetrafluoroethylene, and then separating thetetrafluoroethylene from the mixture.

The following definitional structure is provided for certain terminologyas employed in this specification:

An “alkane” or “alkane compound” is a saturated hydrocarbon compoundhaving the general formula C_(n)H_(2n+2), and may be a straight-chain,branched or cyclic compound. A cyclic compound requires a minimum ofthree carbons.

An “alkene” or “alkene compound” is an unsaturated hydrocarbon compoundthat contains one or more carbon-carbon double bonds, and may be astraight-chain, branched or cyclic compound. An alkene requires aminimum of two carbons. A cyclic compound requires a minimum of threecarbons.

An “aromatic” or “aromatic compound” includes benzene and compounds thatresemble benzene in chemical behavior.

An “azeotropic” composition or “azeotrope composition” is aconstant-boiling mixture of two or more substances that behaves as asingle substance. One way to characterize an azeotropic composition isthat the vapor produced by partial evaporation or distillation of theliquid has the same composition as the liquid from which it isevaporated or distilled, i.e., the mixture distills/refluxes withoutcompositional change. Constant-boiling compositions are characterized asazeotropic because they exhibit either a maximum or minimum boilingpoint, as compared with that of the non-azeotropic mixture of the samecomponents. Azeotropic compositions are also characterized by a minimumor a maximum in the vapor pressure relative to the vapor pressure as afunction of composition at a constant temperature.

An “azeotrope-like” composition is a composition that has aconstant-boiling characteristic or a tendency not to fractionate uponboiling or evaporation. The composition of the vapor formed isconsequently the same as, or substantially the same as, the originalliquid composition. During boiling or evaporation, the liquidcomposition, if it changes at all, changes only to a minimal ornegligible extent. An azeotrope-like composition can also becharacterized by the area that is adjacent to the maximum or minimumvapor pressure in a plot of composition vapor pressure at a giventemperature as a function of mole fraction of components in thecomposition. A composition is azeotrope-like if, after about 50 weightpercent of an original composition is evaporated or boiled off toproduce a remaining composition, the change between the originalcomposition and the remaining composition is no more than about 6 weight%, and is typically about 3 weight % or less, relative to the originalcomposition.

A “high-boiling azeotrope” is an azeotropic or azeotrope- likecomposition that boils at a higher temperature at any given pressurethan any one of the compounds that comprise it would separately boil atthat pressure. Alternatively, a high-boiling azeotrope is any azeotropicor azeotrope-like composition that has a lower vapor pressure at anygiven temperature than any one of the compounds that comprise it wouldseparately have at that temperature.

A “low-boiling-azeotrope” is an azeotropic or azeotrope-like compositionthat boils at a lower temperature at any given pressure than any one ofthe compounds that comprise it would separately boil at that pressure.Alternatively, a low-boiling azeotrope is any azeotropic orazeotrope-like composition that has a higher vapor pressure at any giventemperature than the vapor pressure of any one of the compounds thatcomprise the azeotrope would separately have at that temperature.

An azeotropic or azeotrope-like composition may also be characterized asa substantially constant-boiling admixture under the following criteria,which may vary according to the conditions:

1) The composition can be defined as an azeotrope of two compoundsbecause the term “azeotrope” is at once both definitive and limitative,and requires effective amounts of those two or more compounds for thisunique composition of matter, which can be a constant-boilingcomposition.

2) At different pressures, the composition of a given azeotrope orazeotrope-like composition will vary at least to some degree, as willthe boiling point temperature. Thus, an azeotropic or azeotrope-likecomposition of two compounds represents a unique type of relationshipbut with a variable composition, which depends on temperature and/orpressure. Therefore, compositional ranges, rather than fixedcompositions, are often used to define azeotropes and azeotrope-likecompositions.

3) An azeotrope or azeotrope-like composition of two compounds can becharacterized by a boiling point at a given pressure instead of by aspecific numerical composition, which is limited by and is only asaccurate as the equipment available to perform such an analysis.

Both the boiling point and the weight (or mole) percentages of eachcomponent of an azeotropic composition may change when an azeotrope oran azeotrope-like liquid composition is allowed to boil at differentpressures. Thus, an azeotropic or an azeotrope-like composition may bedefined in terms of the unique relationship that exists among componentsor in terms of the exact weight (or mole) percentages of each componentof the composition characterized by a fixed boiling point at a specificpressure.

The “critical pressure” of a substance is the pressure required toliquefy a gas at its critical temperature, which is the temperature atand above which vapor of the substance cannot be liquefied, regardlessof how much pressure is applied.

A “fluorinated ionic liquid” is an ionic liquid having at least onefluorine on either the cation or the anion, or both. A “fluorinatedcation” or “fluorinated anion” is a cation or anion, respectively,comprising at least one fluorine atom.

A “halogen” is bromine, iodine, chlorine or fluorine.

A “heteroaryl” group is an aryl group having a heteroatom.

A “heteroatom” is an atom other than carbon in the structure of analkanyl, alkenyl, cyclic or aromatic compound.

In “high recovery efficiency”, greater than 90% by weight and mosttypically greater than 95% by weight of the TFE or CO₂ in a mixturethereof is recovered as a product substantially free of the other.

An “impurity”, in a TFE product, is any fluorinated compound other thanthe TFE; and in a CO₂ product, is any inert compound other than the CO₂.

An “ionic liquid” is an organic salt that is fluid at about 100° C. orbelow, as more particularly described in Science (2003) 302:792-793.

A “mass separating agent” (MSA) is a compound useful for the separationof components in an azeotropic or constant- or close-boiling mixture.When used in a process such as extractive distillation, the MSA, as anentrainer, interacts selectively with (but does not chemically reactwith) one or more of the individual components of the mixture. When usedin a process such as absorption, the MSA may function as an absorbentthat is added to aid in the separation of gaseous components ofclose-boiling, constant-boiling or azeotropic mixtures by interactingselectively with (but not reacting with) one or more components withinthe gas mixture. The use and operation of an entrainer or an absorbentis more particularly described in Section 13, “Distillation”, in Perry'sChemical Engineers' Handbook, 7^(th) Ed., (McGraw-Hill, 1997). An MSAmay be used in an “effective amount”, which is typically an amount of atleast one MSA that, in the presence of a desired product and animpurity, causes the volatility of the impurity to increase or decreaserelative to the desired product sufficiently to allow separation bydistillation or absorption of the impurity from the desired product.Alternatively, an effective amount of an MSA is an amount that, in thepresence of a desired product and an impurity, results in the formationof a lower- or higher-boiling azeotropic or azeotrope-like compositionor otherwise causes the volatility of the impurity to increase ordecrease relative to the desired product sufficiently to allowseparation by distillation or absorption of the impurity from thedesired product. An effective amount of an MSA may thus vary dependingon the pressure applied to the mixture to be separated in cases whereazeotrope or azeotrope-like compositions, or changes in the relativevolatility of the components of the mixture, exist.

“Optionally substituted with at least one member selected from the groupconsisting of”, when referring to an alkane, alkene, alkoxy,fluoroalkoxy, perfluoroalkoxy, fluoroalkyl, perfluoroalkyl, aryl orheteroaryl radical or moiety, means that one or more hydrogens on acarbon chain of the radical or moiety may be independently substitutedwith one or more of the members of a recited group of substituents. Forexample, a substituted —C₂H₅ radical or moiety may, without limitation,be —CF₂CF₃, —CH₂CH₂OH or —CF₂CF₂I where the group or substituentsconsist of F, I and OH.

“Selectivity”, “separation factor” or “∝_(ij)” refers to the ratio ofthe infinite activity coefficient of component i to the infiniteactivity coefficient of component j where components i and j are presentat an infinite degree of dilution in a mixture, such as a mixture thatcontains an entrainer and is being subjected to extractive distillation.

“Separating” or “to separate” refers to the removal of a component froma mixture. In various embodiments, separating or to separate may referto the partial or complete removal of a component from the mixture. Ifafter the partial removal of a component, further purification isrequired, one or more additional separation steps may be required toachieve complete removal. The initial, and if desired additional,separation steps may include, for example, one or more of the steps ofdistillation, stripping, rectification, extraction, chromatography,and/or evaporation. Separation may be performed for example by atechnique such as extractive distillation wherein an MSA interactsselectively with (but does not react with) one or more components withinthe mixture, and is typically introduced at an upper feed point of adistillation column, whereas the mixture requiring separation isintroduced at the same or preferably a relatively lower feed point ofthe column than the entraining agent. The MSA passes downwardly throughtrays or packing located in the column and exits the column bottoms withone or more components of the mixture to be separated. While in thepresence of the MSA, at least one of the components to be separatedbecomes relatively more volatile compared to the other component(s) ofthe mixture, with that more volatile component of the initial mixtureexiting the column overhead. MSAs that are fed to a distillation columnat a point equal to, or higher than, the mixture to be separated andwhich pass down through the column thus enabling a separation bydistillation, are also called extractive agents or extractants.

A “vacuum” is a pressure less than 1 bar but greater than 10⁻⁴ bar forpractical use in equipment capable of performing a separation processsuch as extractive distillation.

This invention relates to a process for separating tetrafluoroethylenefrom CO₂ in a mixture thereof. A mixture containing these two componentscan be obtained from, or provided by, any manufacturing process orsource that produces or generates at least one of the components. Forexample, TFE may be produced by reacting chlorodifluoromethane (HCFC-22or R-22) in a pyrolysis furnace, and then CO₂ may be admixed with theTFE product, typically at a concentration of about 50 weight percent (wt%) TFE relative to the concentration of CO₂. The CO₂ inhibits the TFEfrom polymerizing prematurely, which could release a large amount ofheat and could lead to an explosion. The mixture comprising TFE and CO₂may additionally comprise small amounts of impurities, such as HCFC-22or hexafluoropropylene (HFP). CO₂ may be obtained commercially fromvarious vendors such as Air Liquide, or can be obtained from thereaction of steam and a hydrocarbon such as methane, a reaction thatalso produces hydrogen, or produces ammonia if conducted in air.

TFE and CO₂, in their separated and pure states have normal boilingpoints of −75.6 and −78.4° C., respectively. These close boiling pointsalone would make efficient separation of TFE and CO₂ extremely difficultby conventional distillation. However, mixtures of TFE and CO₂ also formazeotropic (96 mol % CO₂ and 4 mol % TFE at −35° C.) and/orazeotrope-like compositions, which makes their complete separation byconventional distillation next to impossible (see, for example, U.S.Pat. No. 5,345,013). Therefore, separating even the azeotropecomposition would require tall and expensive distillation columns, andit would still be extremely difficult to produce substantially pure TFEand CO₂ products without substantial loss of the TFE in the CO₂.

In a process of this invention, TFE is separated from a mixture thereofwith CO₂ using an ionic liquid, or a mixture of ionic liquids, as a massseparating agent. Ionic liquids are organic compounds that are liquid atroom temperature (approximately 25° C.). They differ from most salts inthat they have very low melting points, and they tend to be liquid overa wide temperature range. Many of them are not soluble in non-polarhydrocarbons; are immiscible with water, depending on the anion; andmany of them are highly ionizing (but have a low dielectric strength).Ionic liquids have essentially no vapor pressure, most are air and waterstable, and they can either be neutral, acidic or basic.

A cation or anion of an ionic liquid useful herein can in principle beany cation or anion such that the cation and anion together form anorganic salt that is liquid at or below about 100° C. The properties ofan ionic liquid can, however, be tailored by varying the identity of thecation and/or anion. For example, the acidity of an ionic liquid can beadjusted by varying the molar equivalents and type and combinations ofLewis acids used.

Many ionic liquids are formed by reacting a nitrogen-containingheterocyclic ring, preferably a heteroaromatic ring, with an alkylatingagent (for example, an alkyl halide) to form a quaternary ammonium salt,and performing ion exchange or other suitable reactions with variousLewis acids or their conjugate bases to form the ionic liquid. Examplesof suitable heteroaromatic rings include substituted pyridines,imidazole, substituted imidazole, pyrrole and substituted pyrroles.These rings can be alkylated with virtually any straight, branched orcyclic C₁₋₂₀ alkyl group, but preferably, the alkyl groups are C₁₋₁₆groups, since groups larger than this may produce low melting solidsrather than ionic liquids. Various triarylphosphines, thioethers andcyclic and non-cyclic quaternary ammonium salts may also been used forthis purpose. Counterions that may be used include chloroaluminate,bromoaluminate, gallium chloride, tetrafluoroborate, tetrachloroborate,hexafluorophosphate, nitrate, trifluoromethane sulfonate,methylsulfonate, p-toluenesulfonate, hexafluoroantimonate, hexafluoroarsenate, tetrachloroaluminate, tetrabromoaluminate, perchlorate,hydroxide anion, copper dichloride anion, iron trichloride anion, zinctrichloride anion, as well as various lanthanum, potassium, lithium,nickel, cobalt, manganese, and other metal-containing anions.

Ionic liquids may also be synthesized by salt metathesis, by anacid-base neutralization reaction or by quaternizing a selectednitrogen-containing compound; or they may be obtained commercially fromseveral companies such as Merck (Darmstadt, Germany) or BASF (MountOlive, N.J.).

Representative examples of useful ionic liquids are described in sourcessuch as J. Chem. Tech. Biotechnol., 68:351-356 (1997); Chem. Ind.,68:249-263 (1996); J. Phys. Condensed Matter, 5: (supp 34B):B99-B106(1993); Chemical and Engineering News, Mar. 30, 1998, 32-37; J. Mater.Chem., 8:2627-2636 (1998); Chem. Rev., 99:2071-2084 (1999); and US2004/0133058 (which is incorporated as a part hereof). In one embodimenthereof, a library, i.e. a combinatorial library, of ionic liquids may beprepared, for example, by preparing various alkyl derivatives of thequaternary ammonium cation, and varying the associated anions.

Among the ionic liquids that are suitable for use herein to enhance theseparation of TFE from CO₂ are those that have a lower, and preferably adistinctly lower, solubility and diffusivity for the TFE than the CO₂ inthe mixture. In one embodiment of this invention, ionic liquids suitablefor use herein for such purpose include those having cations describedgenerally by one or more of the following formulae:

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are each independently selected fromthe group consisting of:

-   -   (i) H;    -   (ii) halogen;    -   (iii) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or        cyclic alkane or alkene, optionally substituted with at least        one member selected from the group consisting of Cl, Br, F, I,        OH, NH₂ and SH;    -   (iv)-CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclic        alkane or alkene comprising one to three heteroatoms selected        from the group consisting of O, N, Si and S, and optionally        substituted with at least one member selected from the group        consisting of Cl, Br, F, I, OH, NH₂ and SH;    -   (v) C₆ to C₂₀ unsubstituted aryl, or C₃ to C₂₅ unsubstituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and    -   (vi) C₆ to C₂₅ substituted aryl, or C₃ to C₂₅ substituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S;        wherein said substituted aryl or substituted heteroaryl has one        to three substituents independently selected from the group        consisting of:    -   1. —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclic        alkane or alkene, optionally substituted with at least one        member selected from the group consisting of Cl, Br, F I, OH,        NH₂ and SH,    -   2. OH,    -   3. NH₂, and    -   4. SH; and        wherein R⁷, R⁸, R⁹, and R¹⁰ are each independently selected from        the group consisting of:    -   (vii) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or        cyclic alkane or alkene, optionally substituted with at least        one member selected from the group consisting of Cl, Br, F, I,        OH, NH₂ and SH;    -   (viii) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or        cyclic alkane or alkene comprising one to three heteroatoms        selected from the group consisting of O, N, Si and S, and        optionally substituted with at least one member selected from        the group consisting of Cl, Br, F, I, OH, NH₂ and SH;    -   (ix) C₆ to C₂₅ unsubstituted aryl, or C₃ to C₂₅ unsubstituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S; and    -   (x) C₆ to C₂₅ substituted aryl, or C₃ to C₂₅ substituted        heteroaryl having one to three heteroatoms independently        selected from the group consisting of O, N, Si and S;        wherein said substituted aryl or substituted heteroaryl has one        to three substituents independently selected from the group        consisting of:    -   (1) —CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclic        alkane or alkene, optionally substituted with at least one        member selected from the group consisting of Cl, Br, F, I, OH,        NH₂ and SH,    -   (2) OH,    -   (3) NH₂, and    -   (4) SH; and        wherein optionally at least two of R¹, R², R³, R⁴, R⁵, R⁶, R⁷,        R⁸, R⁹, and R¹⁰ can together form a cyclic or bicyclic alkanyl        or alkenyl group.

In another embodiment, ionic liquids suitable for use herein includethose having fluorinated cations wherein at least one member selectedfrom R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹ and R¹⁰, as described above,comprises F.

In a further embodiment, an ionic liquid suitable for use herein mayhave an anion selected from the group consisting of [CH₃CO₂]⁻, [HSO₄]⁻,[CH₃OSO₃]⁻, [C₂H₅OSO₃]⁻, [AlCl₄]⁻, [CO₃]²⁻, [HCO₃]⁻, [NO₂]⁻, [NO₃]⁻,[SO₄]²⁻, [PO₄]³⁻, [HPO₄]²⁻, [H₂PO₄]⁻, [HSO₃]⁻, [CuCl₂]⁻, Br⁻, I⁻, SCN⁻;and preferably any fluorinated anion. Representative fluorinated anionssuitable for use herein include [BF]⁻, [BF₃CF₃]⁻, [BF₃C₂F₅]⁻, [PF₆]⁻,[PF₃(C₂F₅)₃]⁻, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻,[HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻,[CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻,[CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃]⁻,[(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻; and F⁻. In another embodiment,an ionic liquid herein may comprise a cation selected from the groupconsisting of pyridinium, pyridazinium, pyrimidinium, pyrazinium,imidazolium, pyrazolium, thiazolium, oxazolium, triazolium, phosphonium,and ammonium as defined above; and an anion selected from the groupconsisting of [CH₃CO₂]⁻, [HSO₄]⁻, [CH₃OSO₃]⁻, [C₂HSOSO₃]⁻, [AlCl₄]⁻,[CO₃]²⁻, [HCO₃]⁻, [NO₂]⁻, [NO₃]⁻, [SO₄]²⁻, [PO₄]³⁻, [HPO₄]²⁻, [H₂PO₄]⁻,[HSO₃]⁻, [CuCl₂]⁻, Cl⁻, Br⁻, I⁻, SCN⁻; and any fluorinated anion. In yetanother embodiment, an ionic liquid herein may comprise a cationselected from the group consisting of pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium,oxazolium, triazolium, phosphonium, and ammonium as defined above; andan anion selected from the group consisting of [BF]⁻, [BF₃CF₃]⁻,[BF₃C₂F₅]⁻, [PF₆]⁻, [PF₃(C₂F₅)₃]⁻, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻,[CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻,[(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻,[CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻,[CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻, [CF₃CFHCF₂SO₂)₂N]⁻, and F⁻.

In still another embodiment, an ionic liquid herein may comprise acation selected from the group consisting of pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium,oxazolium, triazolium, phosphonium, and ammonium as defined above,wherein at least one member selected from R¹, R², R³, R⁴, R⁵, R⁶, R⁷,R⁸, R⁹, and R¹⁰ comprises F; and an anion selected from the groupconsisting of [CH₃CO₂]⁻, [HSO₄]⁻, [CH₃OSO₃]⁻, [C₂HSOSO₃]⁻, [AlCl₄]⁻,[CO₃]²⁻, [HCO₃]⁻, [NO₂]⁻, [NO₃]⁻, [SO₄]²⁻, [PO₄]³⁻, [HPO₄]²⁻, [H₂PO₄]⁻,[HSO₃]⁻, [CuCl₂]⁻, Cl⁻, Br, I⁻, SCN⁻, and any fluorinated anion. Instill another embodiment, an ionic liquid herein may comprise a cationselected from the group consisting of pyridinium, pyridazinium,pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium,oxazolium, triazolium, phosphonium, and ammonium as defined above,wherein at least one member selected from R¹, R², R³, R⁴, R⁵, R⁶, R⁷,R⁸, R⁹, and R¹⁰ comprises F⁻; and an anion selected from the groupconsisting of [BF]⁻, [BF₃CF₃]⁻, [BF₃C₂F₅]⁻, [PF₆]⁻, [PF₃(C₂F₅)₃]⁻,[SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻,[(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻,[CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻,[CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃]⁻,[(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻, and F⁻.

In still another embodiment, an ionic liquid suitable for use in thisinvention may include those having:

a) imidazolium as the cation, and an anion selected from the groupconsisting of [BF₄]-, [BF₃CF₃]—, [BF₃C₂F₅]—, [PF₆]—, [PF₃(C₂F₅)₃]—,[SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻,[(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻,[CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻,[CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃]⁻,[(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻, and [CH₃OSO₃]⁻;

b) 1-butyl-3-methylimidazolium as the cation, and an anion selected fromthe group consisting of [BF₄]—, [BF₃CF₃]—, [BF₃C₂F₅]—, [PF₆]—,[PF₃(C₂F₅)₃]—, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻,[HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻,[CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂ SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻,[CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂ SO₃]⁻,[(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻, and [CH₃OSO₃]⁻;

c) 1-ethyl-3-methylimidazolium as the cation, and an anion selected fromthe group consisting of [BF₄]—, [BF₃CF₃]—, [BF₃C₂F₅]—, [PF₆]—,[PF₃(C₂F₅)₃]—, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻,[HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻,[CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻,[CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂ SO₃]⁻,[(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻, and [CH₃OSO₃]⁻;

d) 1-ethyl-3-methylimidazolium as the cation, and [(CF₃CF₂SO₂)₂N]⁻,[PF₆]⁻, or [HCF₂CF₂SO₃]⁻ as the anion;

e) 1,3-dimethylimidazolium as the cation, and an anion selected from thegroup consisting of [BF]—, [BF₃CF₃]—, [BF₃C₂F₅]—, [PF₆]—, [PF₃(C₂F₅)₃]—,[SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻,[(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻,[CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻,[CF₂HCF₂OCF₂CF₂ SO₃]⁻[CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃]⁻,[(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻, and [CH₃OSO₃]⁻.

In various other embodiments of this invention, an ionic liquid formedby selecting any of the individual cations described or disclosedherein, and by selecting any of the individual anions described ordisclosed herein, may be used for the purpose of effecting or enhancingthe separation of TFE from CO₂. Correspondingly, in yet otherembodiments, a subgroup of ionic liquids formed by selecting (i) asubgroup of any size of cations, taken from the total group of cationsdescribed and disclosed herein in all the various different combinationsof the individual members of that total group, and (ii) a subgroup ofany size of anions, taken from the total group of anions described anddisclosed herein in all the various different combinations of theindividual members of that total group, may be used for the purpose ofeffecting or enhancing the separation of TFE from CO₂. In selecting anindividual ionic liquid, or in forming a subgroup of ionic liquids bymaking selections as aforesaid, the ionic liquid or subgroup may be usedin the absence of the members of the group(s) of cations and/or anionsthat are omitted from the total group(s) thereof to make the selection;and, if desirable, the selection may thus be made in terms of themembers of the total group(s) that are omitted from use rather than themembers of the group(s) that are, by the selection, included for use.

In the process of this invention, TFE is separated from a mixturethereof with CO₂ by contacting the mixture with an ionic liquid in whichCO₂ is soluble to a greater extent than TFE. This is advantageousbecause the difference in solubility facilitates the use of a separationtechnique that removes the lower-solubility TFE component from themixture, such as by volatilization, but removes the more-soluble CO₂component (along with the TFE) to a more limited extent, and preferablydoes not remove CO₂ at all. To the extent that it is soluble in theionic liquid, the CO₂ will tend to remain in the mixture as the TFE isbeing removed therefrom.

Separation techniques useful for performing the process of thisinvention include, for example, techniques such as extractivedistillation and absorption. In extractive distillation, as inconventional distillation, at least one component of the mixture iscaused, through temperature and pressure control, to be volatilized in acolumn, and the volatilized component is captured in a separate streamin which it is condensed apart from, and is thus removed from, themixture. At least a portion of this condensed stream can be returned tothe top of the column as reflux, and the remainder recovered as productor for optional processing. The ratio of the condensed material which isreturned to the top of the column as reflux to the material removed asdistillate is referred to as the reflux ratio. The compounds exiting thecolumn as the bottoms stream can be passed to a stripper or seconddistillation column for further separation, and, if desired, compoundsrecovered from the bottoms may then be recycled back to the firstdistillation column for reuse.

The specific conditions applicable to the use of distillation in thisinvention depend on parameters such as the diameter of the distillationcolumn, location of feed points, and the number of separation stages inthe column. The operating pressure of the distillation system may rangefrom about vacuum to about 3.45 MPa (about 500 psia), and may beadjusted in view of the temperatures of the heating and cooling mediaavailable. Normally, increasing the reflux ratio results in increaseddistillate stream purity, but generally the reflux ratio ranges between1/1 to 200/1. The temperature of the condenser, which is locatedadjacent to the top of the column, is normally sufficient tosubstantially fully condense the distillate that is exiting from the topof the column, or is that temperature required to achieve the desiredreflux ratio by partial condensation.

In extractive distillation, there is added to the mixture beingseparated in the column a miscible, high-boiling, relatively nonvolatileMSA that has low latent heat of vaporization, does not form an azeotropewith any of the components in the mixture, and does not chemically reactwith any of the components in the mixture. The MSA is specially chosento interact differently with the various components of the mixture,thereby altering their relative volatilities and “breaking” theazeotrope in which they would otherwise exist. The MSA is thus chosenherein to be an ionic liquid in which the CO₂ component of the mixtureis more soluble, and preferably much more soluble, than the TFEcomponent of the mixture. The TFE component, being less soluble in theMSA may, as a result, be more easily volatilized and separated from themixture than the CO₂ component, which is more soluble in the MSA, whichis functioning as an entrainer. The tendency that the components of anazeotrope would ordinarily have to volatilize in the essentially thesame compositional ratio as they possess in liquid from is thus alteredby the presence of the MSA, which, by solubilizing the CO₂ component ofthe mixture to a greater extent than the TFE component, causes acorresponding change in the compositional content of the stream ofvolatiles liberated from the mixture at a selected temperature andpressure. The TFE component is then removed from the mixture at theselected temperature and pressure as vapor in much higher concentrationthan the CO₂ component, and is preferably removed in essentially pureform uncontaminated with CO₂. The more soluble, less volatile CO₂component remains in the mixture with the MSA, and another criterion forselection of the MSA is that it be an ionic liquid that is easilyseparated from CO₂.

In various embodiments, mixtures of ionic liquids as MSAs may also beuseful for achieving a desired extent of separation. In one embodiment,a mixture of MSAs may be selected wherein one MSA has a high selectivityfor the CO₂ component, and the other MSA has a high capacity tosolubilize the CO₂.

When the separation process of this invention is performed by extractivedistillation, it may be advantageously performed in a distillationcolumn such as is shown in the schematic diagram of FIG. 1. In thecolumn of FIG. 1, separator elements 1 are used for the separation fromthe MSA of the top product, which is the mixture component that is mademore volatile by the presence of the MSA in the mixture. Use of an ionicliquid as the MSA has the advantage of essentially eliminating thepresence of the MSA in the overhead product 7 because of the negligiblevolatility of an ionic liquid.

The flow of the MSA enters at inlet 2, which is preferably located inthe enriching section close to the top of the column below thecondenser, or at the bottom of the rectifying section, wherein anyamount of the MSA that has unexpectedly volatilized is separated fromthe TFE component of the mixture. The ionic liquid as MSA then proceedsin a countercurrent flow direction downward in the column relative tothe upwared flow of the components of the mixture to be separated,especially the lower-solubility TFE. The mixture enters at inlet 4,above the stripping section, where any of the TFE component that isstill admixed with the MSA is finally vaporized. The inlet feed of themixture to be separated may be in liquid or gaseous form, and, if themixture is in liquid form when fed into the column, at least the TFEcomponent thereof will be volatilzed by the temperature and pressureconditions of the column, which will have been selected for thatpurpose. The vapors moving upward in the column are continuouslyenriched in content of the TFE component of the mixture, and the liquidmoving downward in the column is continuously depleted in content ofthat component.

Separator elements 3 and 5 contain a useful number of stages along theheight of the column at which there is thorough gas-liquid contacting,which is desirable for the purpose of obtaining extensive separation ofthe TFE component, which exits the column as the overhead product 7,from the CO₂ component, which exits the column together with the MSA asthe bottom product 6.

Separator elements can be either plates, or ordered or disorderedpackings. In either event, the purpose is to provide a downward cascadeof the MSA, as a liquid entrainer, to contact the rising stream ofvaporized high-volatility component. If plates are used, the liquid mayflow over the edge of one plate onto another, or the liquid may flowthrough the same holes in the plates through which the volatilizedcomponent rises. In either case, the objective is to achieve maximumresidence time of gas-liquid contact consistent with providing a rate ofupward vapor flow that is high enough to prevent the column from beingflooded by the downcoming liquid, but is not so high that the vapor ispushed out of the column without sufficient time to contact the liquid.

There is, in terms of the amount of the mixture to be separated, aminimum amount of the MSA that is needed to “break” the azeotropic, orthe constant- or close-boiling, characteristics of the mixture, andenable the separation of the TFE component from the mixture in a yieldand at a rate that is commercially feasible. In a ratio of the amount ofthe feed of MSA to the amount of feed of the mixture, where the amountof MSA used in the ratio is the minimum amount described above, thevalue of the ratio may in various embodiments be set in a range such asabout 2 to about 4. In other embodiments, feed ratios above 5 may befound to offer no particular advantage in terms of being able to reducethe number of stages in a column. In other embodiments, however, feedratios above or below the ranges described above may be appropriatedepending on the ability of the MSA to preferentially solubilize the CO₂as compared to the TFE. Typically, an increase in the feed rate of theMSA relative to the feed rate of the mixture to be separated, otherthings being equal, does cause an increase in the purity of the TFEproduct to be recovered with regard to the remaining presence of CO₂.

As the separation progresses to conclusion, the MSA is in another stepremoved from the column, as bottoms with the CO₂ component, and the MSAis recycled back to the column for re-entry therein at inlet 2. The MSAmay be separated from the bottom product 6 using various separatingoperations including regeneration by simple evaporation. Thin filmevaporators, such as falling-film or rotary evaporators, are commonlyused for continuous evaporation. In discontinuous concentrationprocesses, two evaporator stages are run alternately so that regeneratedionic liquid, as the MSA, can be returned continuously to thedistillation column. The MSA can also be regenerated by means of astripping column since the vapor pressure of the ionic liquid isessentially zero. A vacuum pump can be used to aid in the separation bylowering the pressure and decreasing the heat input required to degasthe ionic liquid. An alternative means of recovering an ionic liquid asMSA takes advantage of the fact that many ionic liquids can solidifybelow 0° C. In these cases, low cost separation of the ionic liquid canbe achieved by cooling to form a solid phase. The bottom product canalso be precipitated using techniques such as cooling, evaporative, orvacuum crystallization.

An absorption process is typically run with a column similar to thatused in a distillation process except that when contact alone betweenthe ionic liquid MSA and the mixture is sufficient to drive the CO₂component to dissolve in the ionic liquid, a reflux condenser and areboiler may not be needed. The liquid MSA is added at or toward the topof the column, and the vaporized mixture contacts the liquid as it movesup the column while the liquid is moving down. Where, however, the MSAdoes have some degree of volatility itself, it may be desirable to add areflux condenser. Where, at the column operating pressure, reflux occursat an undesirably low temperature, a column with a reboiler may be used.

These and other aspects of extractive distillation and absorption arefurther discussed in sources such as Perry's Chemical Engineers'Handbook, 7^(th) Ed. (Sections 13 and 14, McGraw-Hill, 1997).

The ability to separate a binary mixture of two components i and j canbe determined by calculating their selectivity. The closer theselectivity is to the value of one, the more difficult it is for thecomponents of the mixture to be separated by conventional distillation.Therefore, an extractive distillation or absorption method may be usedto enhance the separation efficiency. In extractive distillation orabsorption, an MSA influences the separation by selectively absorbing ordissolving one or more of the components in the mixture. Where, as inthis invention, an ionic liquid is used as an MSA, the selectivity of anionic liquid for a binary mixture composed of i and j is defined as theratio of the infinite activity coefficient of component i to theinfinite activity coefficient of component j, where components i and jare present at an infinite degree of dilution in the ionic liquid MSA.In general the selectivity can be greater than or less than 1 dependingon whether the low boiler or high boiler is in the numerator. Normallythe low boiler is placed in the numerator so that the selectivity isshown as a value greater than 1. In order to achieve effectiveseparation, a selectivity of greater than about 1.0 is generallyrequired. In one embodiment of the invention, the addition of an ionicliquid to the mixture provides a selectivity greater than about 1.5; andin other embodiments of the invention, the addition of an ionic liquidto the mixture provides a selectivity greater than about 2, greater thanabout 5, greater than about 10, or greater than about 20.

When the separation of this invention is performed by distillation, theindividual components of the mixture may have respective concentrationsranging from about 0.05 to about 99.95 mole percent, relative to thetotal weight of all components in the mixture plus the MSA, depending ontheir location at any particular time in the column. At any particulartime in the process and/or location in the column, the components may besubjected to a temperature in the range of from the reboiler temperatureto the condenser temperature, and a pressure in the range of from vacuumto the critical pressure. Separation processes operate at varying feed,reboiler and condenser temperatures depending on the appropriateconditions for optimum separation. A typical separation process mightoperate with a condenser and/or feed composition chilled by water to atemperature of about 5 to about 10° C., or chilled by brine or ethyleneglycol to even lower temperatures of about 0 to about −40° C. In somecases, if the column operates at close to the normal boiling point of acompound at about 1 atmosphere pressure, the feed and/or the condensercomposition may be cooled to an even lower temperatures of about −40 toabout −80° C. The reboiler can operate over a wide temperature rangedepending on the operating pressure of the column and the identity ofthe compound(s) being separated, which in the case of a fluorinatedcompound such as TFE could be a temperature in the range of from about−80 to about 240° C. The process thus involve steps such as adjusting,by raising or lowering, the temperature and/or pressure of the mixtureand/or the feed of ionic liquid as needed to achieve the desiredseparation.

The separation process of this invention may also be performed by theuse of a kit, which is another embodiment of this invention. A kit,according to this invention, will, for example, include a firstcontainer that contains a mixture of TFE and CO₂, a second containerthat contains one or more ionic liquids, and a connector to connect thefirst container to the second container. A suitable container may be acylindrical metal tank or other pressure vessel, and a suitableconnector may be a hose or tube. The first container includes an outlet,and the second container includes an inlet and an outlet The contents ofthe first container will typically be pressurized since some or all ofthe contents of the first container are to be passed through the secondcontainer.

For that purpose, the connecter is connected to the outlet of the firstcontainer and to the inlet of the second container, and some or all ofthe contents of the first container are introduced into the secondcontainer. After some or all of the contents of the first container havepassed through the second container, they exit the second containerthrough the outlet thereof. For example, some or all of the contents ofthe first container may be bubbled through the second container, and forsuch purpose the inlet on the second container may be at the bottomthereof, and the outlet will be at the top. In other embodiments,however, first container contents may be introduced at other locationson the second container and/or may be introduced by methods such asinjection or pouring. In its interior, the second container includesmeans for contacting the TFE/CO₂ mixture received from the firstcontainer with the ionic liquid residing within the second container.Such contacting means may include perforated piping, spray heads,nozzles, blades, paddles, screws or pumps.

When the connector is attached between the containers, and some or allof the TFE/CO₂ mixture in the first container is passed into and throughthe second container, the CO₂ in the mixture is absorbed into the ionicliquid, and purified TFE is released from the outlet of the secondcontainer. If desired, the TFE produced by separation of it within thesecond container from the mixture with CO₂ may be used to prepare afluorinated polymer or copolymer. Another embodiment of this inventionis consequently a process for preparing a fluorinated polymer orcopolymer by separating TFE from a mixture thereof with CO₂ bycontacting the mixture with one or more ionic liquids, recovering theTFE, and subjecting the TFE to a polymerization reaction to prepare afluorinated polymer or copolymer. A fluorinated polymer or copolymer maybe produced by a process such as emulsion polymerization under pressureusing free radical catalysts such as peroxides or azo compounds, or byother suitable catalysts and conditions selected from those known in theart. The polymer may be a homopolymer such as PTFE; or a copolymerprepared from TFE and monomers such as ethylene or other alpha-olefins;other unsaturated fluorocarbons, hydrofluorocarbons orhydrofluorochlorocarbons; an acrylate; or various vinyl compounds suchas vinyl acetate.

The following examples are presented to illustrate the operation of thisinvention and to assist the artisan in making and using the same. Theseexamples are not intended in any way to limit the scope of thedisclosure or the appended claims. In this work, selectivities are usedin Example 1 to illustrate the extent to which TFE can be separated fromCO₂. Example 2 uses a process simulation program (ASPEN Plus®, AspenTechnology, Inc., Cambridge Mass.) to model the separation of TFE andCO₂ by extractive distillation using the ionic liquid [bmim][PF₆] as anMSA.

General Methods and Materials

1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆],C₈H₁₅N₂F₆P, molecular weight 284 g mol⁻¹), was obtained from FlukaChemika (and may, similarly, be obtained from Sigma-Aldrich, St. Louis,Mo.) with a purity of >97%. Tetrafluoroethylene (TFE, FC-1114, C₂F₄,molecular weight 100.02 g mol⁻¹) was obtained from DuPontFluorochemicals (Wilmington, Del.), with a minimum purity of 99.99%.Carbon dioxide (CO₂, molecular weight 44.01 g mol⁻¹), was obtained fromMG Industries (Allentown, Pennslyvania) with a minimum purity of99.998%.

The syntheses of non-commercially available anions (potassium1,1,2,2-tetrafluoroethanesulfonate,potassium-1,1,2-trifluoro-2-(perfluoroethoxy)ethanesulfonate,potassium-1,1,2-trifluoro-2-(trifluoromethoxy)ethanesulfonate, andsodium 1,1,2,3,3,3-hexafluoropropanesulfonate); and ionic liquids(1-butyl-2,3-dimethylimidazolium 1,1,2,2-tetrafluoroethanesulfonate,1-butyl-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate,1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethane sulfonate,1-ethyl-3-methylimidazolium 1,1,2,3,3,3-hexafluoropropanesulfonate,1-hexyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate,1-dodecyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate,-hexadecyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate,1-octadecyl-3-methylimidazolium 1,1,2,2-tetrafluoroethaneulfonate,1-propyl-3-(1,1,2,2-TFES) imidazolium1,1,2,2-tetrafluoroethanesulfonate, 1-butyl-3-methylimidazolium1,1,2,3,3,3-hexafluoropropanesulfonate, 1-butyl-3-methylimidazolium1,1,2-trifluoro-2-(trifluoromethoxy)ethanesulfonate,1-butyl-3-methylimidazolium1,1,2-trifluoro-2-(perfluoroethoxy)ethanesulfonate,tetradecyl(tri-n-butyl)phosphonium1,1,2,3,3,3-hexafluoropropanesulfonate,tetradecyl(tri-n-hexyl)phosphonium1,1,2-trifluoro-2-(perfluoroethoxy)ethanesulfonate,tetradecyl(tri-n-hexyl)phosphonium1,1,2-trifluoro-2-(trifluoromethoxy)ethanesulfonate,1-ethyl-3-methylimidazolium1,1,2,2-tetrafluoro-2-(pentafluoroethoxy)sulfonate, andtetrabutylphosphonium1,1,2-trifluoro-2-(perfluoroethoxy)ethanesulfonate) is described in U.S.Patent Application No. 60/719,735, which is incorporated in its entiretyas a part hereof for all purposes.

TFE solubility measurements were made using a glass equilibrium cell [E.W. Slocum, Ind. Eng. Chem. Fundam. (1975) 14, 126]. The glassequilibrium cell has a known volume and is agitated so that the upperphase (gas or liquid) mixes into the lower liquid phase. A known amountof ionic liquid is loaded into the cell and evacuated under heating todegas and remove any residual water in the ionic liquid. Knowing thedensity of the ionic liquid, the volume of the ionic liquid can becalculated, and the difference from the initial glass cell volume usedto calculate the vapor space volume. A known amount of gas is fed intothe cell and the temperature is held constant with a circulating oilbath. The pressure of the cell is measured and recorded. When thepressure is determined to no longer change, the cell is at equilibriumand the amount of gas absorbed is calculated by taking into account theamount of gas in the equilibrium cell vapor space. Further discussion ofthis equipment and procedure is available in W. Schotte, Ind. Eng. Chem.Process Des. Dev. (1980) 19, 432-439.

CO₂ solubility measurements were made using a gravimetric microbalance(Hiden, IGA 003, Hiden Isochema Ltd., Warrington, UK). The microbalanceconsists of an electrobalance with sample and counterweight componentsinside a stainless steel pressure-vessel. The balance has a weigh rangeof 0-100 mg with a resolution of 0.1 μg. An enhanced pressure stainlesssteel (SS316LN) reactor capable of operation to 2.0 MPa and 100° C. wasinstalled. Approximately 60 mg of ionic liquid sample was added to thesample container and the reactor was sealed. The sample was dried anddegassed by first pulling a course vacuum on the sample with a diaphragmpump (Pfeiffer, model MVP055-3, Asslar, Germany) and then fullyevacuating the reactor to 10⁻⁹ MPa with a turbopump (Pfeiffer, modelTSH-071). While under deep vacuum, the sample was heated to 75° C. for10 h with an external water jacket connected to a remote-controlledconstant-temperature bath (Huber Ministat, model cc-S3, Offenburg,Germany). A 30 percent ethylene glycol and 70 percent water mixture byvolume was used as the recirculating fluid with a temperature range of 5to 90° C. The sample mass slowly decreased as residual water and gasesare removed. Once the mass had stabilized for at least 60 min, thesample dry mass was recorded. The IGA003 can operate in both dynamic andstatic mode. Dynamic mode operation provides a continuous flow of gas(max. 500 cm³ min⁻¹) past the sample and the exhaust valve controls theset-point pressure. Static mode operation introduces gas into the top ofthe balance away from the sample and both the admittance and exhaustvalves control the set-point pressure. All absorption measurements wereperformed in static mode. The sample temperature was measured with atype K thermocouple with an accuracy of ±0.1° C. The thermocouple waslocated inside the reactor next to the sample container. The waterjacket maintained the set-point temperature automatically to within atypical regulation accuracy of ±0.1° C. Four isotherms (at 10, 25, 50,and 75° C.) were measured beginning with 10° C. Once the desiredtemperature was achieved and stable, the admittance and exhaust valveswill automatically open and close to adjust the pressure to the firstset-point. Pressures from 10⁻¹⁰ to 10⁻² MPa were measured using acapacitance manometer (Pfeiffer, model PKR251), and pressures from 10⁻²to 2.0 MPa were measured using a piezo-resistive strain gauge (Druck,model PDCR4010, New Fairfield, Conn.). Regulation maintained the reactorpressure set-point to within ±4 to 8 kPa. The pressure ramp rate was setat 200 kPa min⁻¹, and the temperature ramp rate was set at 1° C. min⁻¹.The upper pressure limit of the stainless steel reactor was 2.0 MPa, andseveral isobars up to 2.0 MPa (i.e. 0.1, 0.5, 1, 4, 7, 10, 13, 15, and20 bar) were measured. To ensure sufficient time for gas-liquidequilibrium, the ionic liquid samples were maintained at set-point for aminimum of 3 h with a maximum time-out of 12 h. Further discussion ofthis equipment and procedure is available in M. B. Shiflett and A.Yokozeki, Ind. Eng. Chem. Res. (2005) 44(12), 4453-4464.

Example 1 Separation of a Mixture Containing Tetrafluoroethylene (TFE)and Carbon Dioxide (CO₂)

This example addresses thermodynamic properties at the infinite dilutionstate. Activity coefficients at infinite dilution γ^(∞) were analyzedfor TFE and CO₂ in [bmim][PF₆].

Solubility (PTx) data for TFE and CO₂ in [bmim][PF₆] are summarized inExamples 3 and 4. Data have been correlated with theNon-Random-Two-Liquid (NRTL) solution model.

The NRTL activity coefficient (γ_(i)) model for a binary system is givenby:

$\begin{matrix}{{{\ln \; \gamma_{1}} = {x_{2}^{2}\left\lbrack {{\tau_{21}\left( \frac{G_{21}}{x_{1} + {x_{2}G_{21}}} \right)}^{2} + \frac{\tau_{12}G_{12}}{\left( {x_{2} + {x_{1}G_{12}}} \right)^{2}}} \right\rbrack}},} & (1) \\{{{\ln \; \gamma_{2}} = {x_{1}^{2}\left\lbrack {{\tau_{12}\left( \frac{G_{12}}{x_{2} + {x_{1}G_{12}}} \right)}^{2} + \frac{\tau_{21}G_{21}}{\left( {x_{1} + {x_{2}G_{21}}} \right)^{2}}} \right\rbrack}},} & (2)\end{matrix}$

where

G ₁₂≡exp(−ατ₁₂), and G ₂₁≡exp(−ατ₂₁),  (3)

τ₁₂ and τ₂₁: adjustable binary interaction parameters.  (4)

α=0.2 (assumed to be a constant of 0.2 in this work).

The temperature-dependent binary interaction parameter (τ_(ij)) ismodeled by:

τ_(ij)=τ_(ij) ⁽⁰⁾+τ_(ij) ⁽¹⁾ /T  (5

Vapor liquid equilibria (VLE) are obtained by solving the followingequations:

y _(i) PΦ _(i) ≡x _(i)γ_(i) P _(i) ^(S), (i=1 for TFE and i=2 for ionicliquid)  (6)

In the present system, it can be assumed that P₂ ^(S)≈0 and y₂≈0 (ory₁≈1). Then, eq 6 becomes only one equation with i=1, and the correctionfactor for non-ideality, Φ₁, can be written as:

$\begin{matrix}{\Phi_{1} = {{\exp\left\lbrack \frac{\left( {B_{11} - \overset{\_}{V_{1}}} \right)\left( {P - P_{1}^{S}} \right)}{RT} \right\rbrack}.}} & (7)\end{matrix}$

The second virial coefficient, B₁₁ (1), of pure species 1 can becalculated with proper equation-of-state models, and the saturated molarliquid volume, V ₁ (T), is calculated using the method described inShiflett, M. B.; Yokozeki, A. Solubility and Diffusivity ofHydrofluorocarbons in Room-Temperature Ionic Liquids. AIChE J. (2006),52, 1205. The vapor pressure of pure species 1 is modeled by:

$\begin{matrix}{{\log_{10}P_{1}^{S}} = {A_{1} - {\frac{B_{1}}{T + C_{1}}.}}} & (8)\end{matrix}$

The coefficients in eq 8 for TFE are (A₁=7.90353, B₁=2012.94, C₁=1.2044)and CO₂ are (A₁=12.3312, B₁=4759.46, C₁=156.462) and it is assumed thateq 8 holds even above VLE (vapor liquid equilibrium) criticaltemperature T as an extrapolated hypothetical vapor pressure.

The present solubility model contains maximum four adjustableparameters: τ₁₂ ⁽⁰⁾, τ₁₂ ⁽¹⁾, τ₂₁ ⁽⁰⁾, and τ₂₁ ⁽¹⁾. These parametershave been determined using non-linear least-squares analysis with anobjective function of: Σ_(i=1) ^(N)(1−P_(obs)(i)/P_(calc)(i))² N datapoints. Optimal values for these parameters for TFE are τ₁₂ ⁽⁰⁾=1.0662,τ₁₂ ⁽¹⁾=339.40 K, τ₂₁ ⁽⁰⁾=4.5270, and τ₂₁ ⁽¹⁾=−805.60 K. Optimal valuesfor these parameters for CO₂ are τ₁₂ ⁽⁰⁾=−4.663, τ₁₂ ⁽¹⁾=2806.8 K, τ₂₁⁽⁰⁾=1.0656, and τ₂₁ ⁽¹⁾=812.37 K.

Although the infinite dilution state is only a limited (or extrapolated)state of actual solutions, the thermodynamic properties at such a stateprovide important physical/chemical understandings about solute andsolvent interactions. Activity coefficients at infinite dilution, γ₁^(∞), of TFE and CO₂ in [bmim][PF₆] can be derived from eq 1 by settingx₁=0 and x₂=1.

ln γ₁ ²⁸=τ₂₁+τ₁₂ G ₁₂.  (11)

Table 1 provides temperature (T), the saturated vapor pressure (P_(i)^(S)), the 2^(nd) virial coefficient (B₁₁), and the activity coefficientat infinite dilution (γ₁ ^(∞)) for TFE and CO₂ in [bmim][PF₆].

TABLE 1 T P_(i) ^(S) B₁₁ Gas (K) (MPa) (cm³ mol⁻¹) γ_(l) ^(∞) TFE 287.922.5634 −673.62 23.61 TFE 328.29 6.0156 −612.58 31.58 CO₂ 283.15 4.4917−138.57 1.04 CO₂ 298.15 6.4361 −123.01 1.22 CO₂ 323.15 11.1077 −102.061.49 CO₂ 348.15 18.1611 −85.49 1.71

These activity coefficients at infinite dilution γ₁ ^(∞) were used tocalculate the selectivity (α_(ij)):

$\alpha_{ij} = \frac{\gamma_{i}^{\infty}}{\gamma_{j}^{\infty}}$

where components i and j are present at an infinite degree of dilutionin the entrainer [bmim][PF₆] and i can represent TFE, and j canrepresent CO₂. In order to achieve separation, a selectivity of greaterthan about 1.0 is preferred. The selectivities (α_(ij)) in Table 2 showthat the use of [bmim][PF₆] as an entrainer will separate TFE and CO₂with a selectivity of greater than 20 over a temperature from 283.15 to348.15 K.

TABLE 2 T (K) γ_(i) ^(∞) γ_(j) ^(∞) α_(ij) 283.15 22.66 1.04 21.8 298.1525.62 1.22 21.0 323.15 30.56 1.49 20.5 348.15 35.49 1.71 20.7

Example 2 Separation of a Mixture Comprising Tetrafluoroethylene andCarbon Dioxide

An Aspen Plus® process simulation was used to model the separation of amixture containing tetrafluoroethylene (TFE) and carbon dioxide (CO₂) byextractive distillation using [bmim][PF₆] as the entrainer. The Aspenflowsheet used for this simulation consists of an extraction columnmodeled with RadFrac and a single stage stripping unit modeled as aflash drum for the regeneration of the ionic liquid (IL), which isrecycled back into the main column as shown in FIG. 1.

The immeasurable vapor pressure of the ionic liquid was taken intoconsideration by fitting the extended Antoine equation value close tozero. The ionic liquid was treated as a non-dissociating component andassumption of an ideal vapor phase was made, therefore, the investigatedvapor-liquid equilibrium (VLE) data could be described by the liquidconcentration and activity coefficient. Nonrandom two-liquid (NRTL)binary interaction parameters [S. I., Sandler, Chemical and EngineeringThermodynamics, 3^(rd) Edition (1999) John Wiley and Sons, Inc., NewYork, Chapter 7] between the components and the ionic liquid weregenerated using (P, T, x) data obtained from solubility experiments (seeExamples 3 and 4 for solubility data for TFE and CO₂, respectively, in[bmim][PF₆]). Aspen was used to regress the NRTL parameters from the (P,T, x) data.

The extraction column consists of 20 theoretical stages, including thepartial condenser and reboiler, and operates at 793 kPa (115 psia). Thefeed is a 50 wt % TFE and 50 wt % CO₂ at 25° C., which is fed into thecolumn at stage 9. The ionic liquid is fed at approximately a 40:1 massratio relative to the feed through the second stage of the column at 25°C. The column operates with a mass reflux ratio of 1.5. As shown inTable 3, 98% of the TFE fed into the main column is recovered as a vapordistillate from this column, with a purity of 99.73 wt %. The remainingTFE and essentially all of the CO₂ leave out the column bottom alongwith the ionic liquid.

The bottoms stream from the extraction column is sent to a flash drumoperating at 2 psia and 180° C. This flash strips the CO₂ and residualTFE from the ionic liquid being recycled, reducing its impurity leveldown to nominally 300 ppmw CO₂ and 1 ppmw TFE.

TABLE 3 Aspen Results Extraction Column Feeds Ionic Liquid (IL) (kg/hr)4000 TFE/CO₂ (kg/hr) 100 TFE/CO₂ Composition 50 wt % TFE/50 wt % CO2TFE/CO₂ gas mixture Temp. (K) 298.15 Ionic Liquid (IL) Temp. (K) 298.15Extraction Column Distillate, overhead (kg/hr) 49 Distillate purity (wt% TFE) 99.73% Product Yield   98% Bottoms flow (kg/hr) 4051 Theoreticalstages 20 Operating pressure (psia) 115 Reflux ratio (mass basis) 1.5Ionic Liquid stage 2 TFE/CO₂ Feed stage 9 Condenser Temperature (K)245.85 K Reboiler Temperature (K) 332.55 K Condenser duty (BTU/hr)−14,300 Reboiler duty (BTU/hr) 195,000 Stripper Flash Tank Operatingpressure (psia) 2 Operating Temperature (K) 453.15 CO₂, Overhead purity(x_(W2))  99.1% Ionic Liquid, Recycle (kg/hr) 4000.02 kg/hr IonicLiquid, Recycle purity 99.97% Heat duty (BTU/hr) 700,000 Solvent CoolerHeat Duty (BTU/hr) −871,000

Examples 3 and 4 provide solubility results for tetrafluoroethylene(TFE) and carbon dioxide (CO₂), respectively. These data are used forcalculating the activity coefficient at infinite dilution (γ₁ ^(∞)) asshown in Example 1 and the NRTL parameters for ASPEN® process modelingin Example 2.

Example 3 Solubility of tetrafluoroethylene (TFE) in1-butyl-3-methylimidazolium hexafluorophosphate

A solubility study was made at temperatures of 14.77 and 55.14° C. overa pressure range from 0 to about 1.4 MPa where the solubilities(x_(meas.)) were measured using a volumetric view cell. Tables 4a and 4bprovide data for T, P, and x_(meas) at temperatures of 14.77 and 55.14°C., respectively.

TABLE 4a T P x_(meas.) (° C.) (MPa) (mole %) 14.77 0.0713 0.2494 14.770.1762 0.6096 14.77 0.3020 1.0300 14.77 0.4473 1.4890 14.77 0.58371.9100 14.77 0.7400 2.3770 14.77 0.9012 2.8450 14.77 1.0463 3.3100

TABLE 4b T P x_(meas.) (° C.) (MPa) (mole %) 55.14 0.1398 0.2938 55.140.2813 0.5711 55.14 0.4316 0.8571 55.14 0.5680 1.1110 55.14 0.70441.3590 55.14 0.8526 1.6250 55.14 0.9903 1.8640 55.14 1.1322 2.1050 55.141.2727 2.3360 55.14 1.4192 2.5730

Example 4 Solubility of carbon dioxide (CO₂) in1-butyl-3-methylimidazolium hexafluorophosphate

A solubility study was made at temperatures of 10.0, 25.0, 50.0, and75.0° C. over a pressure range from 0 to about 2.0 MPa where thesolubilities (x_(meas.)) were measured using a gravimetric microbalance.Tables 5a, 5b, 5c, and 5d provide data for T, P, and x_(meas) attemperatures of 10.0, 25.0, 50.0, and 75.0° C., respectively.

TABLE 5a T P x_(meas.) (° C.) (MPa) (mole %) 9.9 0.0097 0.4 9.9 0.05011.6 9.9 0.1002 2.9 10.4 0.3996 10.2 10.6 0.6996 16.7 10.5 1.0000 22.48.9 1.3003 28.4 9.9 1.4998 30.9 9.9 1.9998 37.9

TABLE 5b T P x_(meas.) (° C.) (MPa) (mole %) 24.9 0.0102 0 24.9 0.05020.9 24.9 0.1002 1.8 25.0 0.3996 7.2 25.0 0.7000 12.2 24.9 0.9994 16.724.9 1.2999 20.8 24.9 1.4994 23.3 24.9 1.9992 29.1

TABLE 5c T P x_(meas.) (° C.) (MPa) (mole %) 50.1 0.0102 0.2 50.0 0.05030.6 50.0 0.1002 1.2 50.1 0.3996 4.7 50.0 0.7000 7.9 50.0 0.9998 10.950.0 1.3002 13.6 50.1 1.5003 15.5 50.0 1.9998 19.7

TABLE 5d T P x_(meas.) (° C.) (MPa) (mole %) 75.0 0.0102 0.1 74.9 0.05010.2 74.9 0.1000 0.7 74.9 0.3997 3.2 74.9 0.7000 5.6 74.8 1.0002 7.8 75.01.3003 9.9 74.9 1.4999 11.3 75.1 1.9995 14.9

In this specification, unless explicitly stated otherwise or indicatedto the contrary by the context of usage, where an embodiment of thesubject matter hereof is stated or described as comprising, including,containing, having, being composed of or being constituted by or ofcertain features or elements, one or more features or elements inaddition to those explicitly stated or described may be present in theembodiment. An alternative embodiment of the subject matter hereof,however, may be stated or described as consisting essentially of certainfeatures or elements, in which embodiment features or elements thatwould materially alter the principle of operation or the distinguishingcharacteristics of the embodiment are not present therein. A furtheralternative embodiment of the subject matter hereof may be stated ordescribed as consisting of certain features or elements, in whichembodiment, or in insubstantial variations thereof, only the features orelements specifically stated or described are present.

1. A process for separating tetrafluoroethylene from a mixturecomprising tetrafluoroethylene and carbon dioxide, comprising contactingthe mixture with at least one ionic liquid in which carbon dioxide issoluble to a greater extent than tetrafluoroethylene, and separating thetetrafluoroethylene from the mixture.
 2. The process of claim 1 whereinan ionic liquid has a cation selected from the group consisting of thefollowing eleven cations:

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are independently selected from thegroup consisting of: (i) H (ii) halogen (iii) —CH₃, —C₂H₅, or C₃ to C₂straight-chain, branched or cyclic alkane or alkene, optionallysubstituted with at least one member selected from the group consistingof Cl, Br, F, I, OH, NH₂ and SH; (iv) —CH₃, —C₂H₅, or C₃ to C₂₅straight-chain, branched or cyclic alkane or alkene comprising one tothree heteroatoms selected from the group consisting of O, N and S, andoptionally substituted with at least one member selected from the groupconsisting of Cl, Br, F, I, OH, NH₂ and SH; (v) C₆ to C₂₀ unsubstitutedaryl, or C₃ to C₂₅ unsubstituted heteroaryl having one to threeheteroatoms independently selected from the group consisting of O, N andS; and (vi) C₆ to C₂₅ substituted aryl, or C₃ to C₂₅ substitutedheteroaryl having one to three heteroatoms independently selected fromthe group consisting of O, N and S; and wherein said substituted aryl orsubstituted heteroaryl has one to three substituents independentlyselected from the group consisting of: (1) —CH₃, —C₂H₅, or C₃ to C₂₅straight-chain, branched or cyclic alkane or alkene, optionallysubstituted with at least one member selected from the group consistingof Cl, Br, F I, OH, NH₂ and SH, (2) OH, (3) NH₂, and (4) SH; R⁷, R⁸, R⁹,and R¹⁰ are independently selected from the group consisting of: (vii)—CH₃, —C₂H₅, or C₃ to C₂₅ straight-chain, branched or cyclic alkane oralkene, optionally substituted with at least one member selected fromthe group consisting of Cl, Br, F, I, OH, NH₂ and SH; (viii)-CH₃, —C₂H₅,or C₃ to C₂₅ straight-chain, branched or cyclic alkane or alkenecomprising one to three heteroatoms selected from the group consistingof O, N and S, and optionally substituted with at least one memberselected from the group consisting of Cl, Br, F, I, OH, NH₂ and SH; (ix)C₆ to C₂₅ unsubstituted aryl, or C₃ to C₂₅ unsubstituted heteroarylhaving one to three heteroatoms independently selected from the groupconsisting of O, N and S; and (x) C₆ to C₂₅ substituted aryl, or C₃ toC₂₅ substituted heteroaryl having one to three heteroatoms independentlyselected from the group consisting of O, N and S; and wherein saidsubstituted aryl or substituted heteroaryl has one to three substituentsindependently selected from the group consisting of: (1) —CH₃, —C₂H₅, orC₃ to C₂₅ straight-chain, branched or cyclic alkane or alkene,optionally substituted with at least one member selected from the groupconsisting of Cl, Br, F, I, OH, NH₂ and SH, (2) OH, (3) NH₂, and (4) SH;and wherein optionally at least two of R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸,R⁹, R¹⁰ can together form a cyclic or bicyclic alkanyl or alkenyl group.3. The process of claim 1 wherein at least one of R¹, R², R³, R⁴, R⁵,R⁶, R⁷, R⁸, R⁹, and R¹⁰ comprises F⁻.
 4. The process of claim 1 whereinan ionic liquid comprises an anion selected from the group consisting of[CH₃CO₂]⁻, [HSO₄]⁻, [CH₃OSO₃]⁻, [C₂HSOSO₃]⁻, [AlCl₄]⁻, [CO₃]²⁻, [HCO₃]⁻,[NO₂]⁻, [NO₃]⁻, [SO₄]²⁻, [PO₄]³⁻, [HPO₄]²⁻, [H₂PO₄]⁻, [HSO₃]⁻, [CuCl₂]⁻,Cl⁻, Br⁻, I⁻, SCN⁻, and any fluorinated anion.
 5. The process of claim 2wherein an ionic liquid comprises an anion selected from the groupconsisting of [CH₃CO₂]⁻, [HSO₄]⁻, [CH₃OSO₃]⁻, [C₂H_(S)OSO₃]⁻, [AlCl₄]⁻,[CO₃]²⁻, [HCO₃]⁻, [NO₂]⁻, [NO₃]⁻, [SO₄]²⁻, [PO₄]³⁻, [HPO₄]²⁻, [H₂PO₄]⁻,[HSO₃]⁻, [CuCl₂]⁻, Cl⁻, Br⁻, I⁻, SCN⁻, and any fluorinated anion.
 6. Theprocess of claim 3 wherein an ionic liquid comprises an anion selectedfrom the group consisting of [CH₃CO₂]⁻, [HSO₄]⁻, [CH₃OSO₃]⁻,[C₂HSOSO₃]⁻, [AlCl₄]⁻, [CO₃]²⁻, [HCO₃]⁻, [NO₂]⁻, [NO₃]⁻, [SO₄]²⁻,[PO₄]³⁻, [HPO₄]²⁻, [H₂PO₄]⁻, [HSO₃]⁻, [CuCl₂]⁻, Cl⁻, Br, I⁻, SCN⁻, andany fluorinated anion.
 7. The process of claim 1 wherein an ionic liquidcomprises an anion selected from the group consisting of [BF]⁻,[BF₃CF₃]⁻, [BF₃C₂F₅]⁻, [PF₆]⁻, [PF₃(C₂F₅)₃]⁻, [SbF₆]⁻, [CF₃SO₃]⁻,[HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻,[(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻,[CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻,[CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃]⁻, [CF₂HCF₂SO₂)₂N]⁻,[(CF₃CFHCF₂SO₂)₂N]⁻, and F⁻.
 8. The process of claim 2 wherein an ionicliquid comprises an anion selected from the group consisting of [BF]⁻,[BF₃CF₃]⁻, [BF₃C₂F₅]⁻, [PF₆]⁻, [PF₃(C₂F₅)₃]⁻, [SbF₆]⁻, [CF₃SO₃]⁻,[HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻,[(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻,[CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻,[CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻,[(CF₃CFHCF₂SO₂)₂N]⁻, and F⁻.
 9. The process of claim 3 wherein an ionicliquid comprises an anion selected from the group consisting of [BF]⁻,[BF₃CF₃]⁻, [BF₃C₂F₅]⁻, [PF₆]⁻, [PF₃(C₂F₅)₃]⁻, [SbF₆]⁻, [CF₃SO₃]⁻,[HCF₂CF₂SO₃]⁻, [CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻,[(CF₃CF₂SO₂)₂N]⁻, [(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻,[CF₃CF₂OCFHCF₂SO₃]⁻, [CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻,[CF₂ICF₂OCF₂CF₂SO₃]⁻, [CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻,[CF₃CFHCF₂SO₂)₂N]⁻, and F⁻.
 10. The process of claim 1 wherein an ionicliquid comprises imidazolium as the cation; and comprises an anionselected from the group consisting of [BF]⁻, [BF₃CF₃]⁻, [BF₃C₂F₅]⁻,[PF₆]⁻, [PF₃(C₂F₅)₃]⁻, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻,[CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻,[(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻,[CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻,[CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻, and[CH₃OSO₃]⁻.
 11. The process of claim 1 wherein an ionic liquid comprises1-butyl-3-methylimidazolium as the cation; and comprises an anionselected from the group consisting of [BF]—, [BF₃CF₃]—, [BF₃C₂F₅]—,[PF₆]—, [PF₃(C₂F₅)₃]—, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻,[CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻,[CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻,[CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻,[CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻ and[CH₃OSO₃]⁻.
 12. The process of claim 1 wherein an ionic liquid comprises1-1-ethyl-3-methylimidazolium as the cation; and comprises an anionselected from the group consisting of [BF]—, [BF₃CF₃]—, [BF₃C₂F₅]—,[PF₆]—, [PF₃(C₂F₅)₃]—, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻,[CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻,[(CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻,[CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻,[CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻ and[CH₃OSO₃]⁻.
 13. The process of claim 1 wherein an ionic liquid comprises1-ethyl-3-methylimidazolium as the cation, and comprises an anionselected from the group consisting of [(CF₃CF₂SO₂)₂N]⁻, [PF₆]⁻ and[HCF₂CF₂SO₃]⁻.
 14. The process of claim 1 wherein an ionic liquidcomprises 1-1,3-dimethylimidazolium as the cation; and comprises ananion selected from the group consisting of [BF₄]—, [BF₃CF₃]—,[BF₃C₂F₅]—, [PF₆]—, [PF₃(C₂F₅)₃]—, [SbF₆]⁻, [CF₃SO₃]⁻, [HCF₂CF₂SO₃]⁻,[CF₃HFCCF₂SO₃]⁻, [HCClFCF₂SO₃]⁻, [(CF₃SO₂)₂N]⁻, [(CF₃CF₂SO₂)₂N]⁻,[CF₃SO₂)₃C]⁻, [CF₃CO₂]⁻, [CF₃OCFHCF₂SO₃]⁻, [CF₃CF₂OCFHCF₂SO₃]⁻,[CF₃CFHOCF₂CF₂SO₃]⁻, [CF₂HCF₂OCF₂CF₂SO₃]⁻, [CF₂ICF₂OCF₂CF₂SO₃]⁻,[CF₃CF₂OCF₂CF₂SO₃]⁻, [(CF₂HCF₂SO₂)₂N]⁻, [(CF₃CFHCF₂SO₂)₂N]⁻ and[CH₃OSO₃]⁻.
 15. The process of claim 1 which is performed in adistillation or absorption column.
 16. The process of claim 15 whereinthe TFE is removed from the top of the column.
 17. The process of claim15 wherein an ionic liquid and CO₂ are removed together from the bottomof the column, the ionic liquid and CO₂ are separated outside thecolumn, and the separated ionic liquid is returned to the column.
 18. Aprocess according to claim 1 further comprising the steps of recoveringthe TFE, and subjecting the TFE to a polymerization reaction to preparea fluorinated polymer or copolymer. 19-22. (canceled)